Low stress overtravel stop

ABSTRACT

A microelectromechanical system device is described. The microelectromechanical system device can comprise: a proof mass coupled to an anchor via a spring, wherein the proof mass moves in response to an imposition of an external load to the proof mass, and an overtravel stop comprising a first portion and a second portion.

TECHNICAL FIELD

The subject disclosure provides improvements to stiction lifetimerobustness in regard to low stress overtravel stops.

BACKGROUND

Lifetime stiction can be a primary concern for customers ofmicroelectromechanical systems (MEMS) devices. Known issues with MEMSdevices are that upon experiencing shocks, these devices can undergochipping at corners when moving structures contact a target. This canlead to undesirable effects, shortening the lifetimes of MEMS devicesand increasing costs and other unforeseen deterioration. Overtravelstops (or bumpstops) have typically been used to reduce the impactexperienced by MEMS devices.

For lifetime stiction testing, overtravel stops can be subjected toapproximately 100,000 impacts. These impacts can degrade anyanti-stiction coatings that can have been applied to the overtravelstops and can consequently lead or result in stiction.

SUMMARY

The following presents a simplified summary of the specification toprovide a basic understanding of some aspects of the specification. Thissummary is not an extensive overview of the specification. It isintended to neither identify key or critical elements of thespecification nor delineate any scope particular to any embodiments ofthe specification, or any scope of the claims. Its sole purpose is topresent some concepts of the specification in a simplified form as aprelude to the more detailed description that is presented later.

In accordance with various embodiments set forth herein, the subjectdisclosure provides a microelectromechanical system device, comprising:a proof mass coupled to an anchor via a spring, wherein the proof massmoves in response to an imposition of an external load to the proofmass, and an overtravel stop comprising a first portion and a secondportion. In various embodiments, when the proof mass contacts the firstportion of the overtravel stop and the proof mass becomes can disengagefrom the second portion of the overtravel stop in response to theexternal load being above a first threshold value and below a secondthreshold value. Further, when the proof mass contacts the secondportion of the overtravel stop and the proof mass can disengage from thefirst portion of the overtravel stop in response to the external loadexceeding the second threshold value. Additionally, the proof mass movesin a first direction in response to the external load being less than afirst threshold value, and the proof mass moves in a second directionwhen the external load exceeds the first threshold value. Furthermore,the first direction can be a first translation or first rotation, andthe second direction can be a second translation or a second rotation.In addition, the first direction can be substantially and/orapproximately orthogonal to the second direction.

Additionally, the overtravel stop can be located on an axis of thesecond direction, and the proof mass can be asymmetric about an axis ofthe second direction. Moreover, the second portion of the overtravelstop can be curved and can have an aspect ratio greater than 1:5. Insome embodiments, a surface of the overtravel stop can comprise any ofsilicon, titanium, germanium, silicon oxide, silicon nitride, tungsten,or titanium nitride. In addition, the microelectromechanical systemdevice can comprise a first sensor and a second sensor, wherein thefirst sensor measures a first motion of the proof mass in a firstdirection, and wherein the second sensor measures a second motion of theproof mass in a second direction.

In accordance with additional and/or alternative embodiments the subjectdisclosure provides a microelectromechanical system device, comprising:a first proof mass coupled to an anchor via a first spring, a secondproof mass coupled to the first proof mass via a second spring, whereinthe first proof mass and the second proof mass moves in response to animposition of an external load, and an overtravel stop comprising afirst portion and a second portion.

In certain embodiments, the second proof mass can contact the firstportion of the overtravel stop and the second proof mass can bedisengaged from the second portion of the overtravel stop in responsethe external load being above a first threshold value and below a secondthreshold value. Further, the second proof mass can contact the secondportion of the overtravel stop and the second proof mass can disengagefrom the first portion of the overtravel stop in response to theexternal load being above the second threshold. Furthermore, the firstproof mass and the second proof mass can move in a first direction whenthe external load is less than a first threshold value, and the secondproof mass can move in a second direction in response to the externalload exceeding the first threshold value. Additionally, the firstdirection can be a first translation or a first rotation, and the seconddirection can be a second translation or a second rotation, such thatthe first direction is substantially orthogonal to the second direction.

In some embodiments the overtravel stop can be located on a first axisassociated with the first direction, and/or the overtravel stop can belocated on a second axis associated with the second direction. Incertain embodiments the first proof mass can be asymmetric about thesecond axis. In additional and/or alternative embodiments themicroelectromechanical system device can further comprise a firstsensing element device and a second sensing element device, wherein thefirst sensing element device measures a first motion of the first proofmass in the first direction, and the second sensing element devicemeasures a second motion of the second proof mass in the seconddirection.

The following description and the annexed drawings set forth certainillustrative aspects of the specification. These aspects are indicative,however, of but a few of the various ways in which the principles of thespecification may be employed. Other advantages and novel features ofthe specification will become apparent from the following detaileddescription of the specification when considered in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous aspects, embodiments, objects and advantages of the presentdisclosure will be apparent upon consideration of the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like reference characters refer to like parts throughout, and inwhich:

FIG. 1 illustrates a low stress overtravel stop, in accordance withvarious embodiments set forth in this disclosure.

FIG. 2 provides additional depiction of a low stress overtravel stop, inaccordance with various embodiments set forth in this disclosure.

FIG. 3 illustrates provides yet a further illustration of a low stressovertravel stop, in accordance with various embodiments set forth inthis disclosure.

FIG. 4 illustrates another a low stress overtravel stop, in accordancewith various embodiments set forth in this disclosure.

FIG. 5 illustrates a still further low stress overtravel stop, inaccordance with various embodiments set forth in this disclosure.

FIG. 6 illustrates an additional low stress overtravel stop, inaccordance with various embodiments set forth in this disclosure.

DETAILED DESCRIPTION

One or more embodiments are now described with reference to thedrawings, wherein like reference numerals are used to refer to likeelements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the various embodiments. It may be evident,however, that the various embodiments can be practiced without thesespecific details, e.g., without applying to any particular networkedenvironment or standard. In other instances, well-known structures anddevices are shown in block diagram form in order to facilitatedescribing the embodiments in additional detail.

FIG. 1 , in accordance with various embodiments, depicts an illustrativeembodiment 100 of a low stress overtravel stop (e.g., low stress elasticbump, or low stress bump stop) that can comprise a first portion 102Aand a second portion 1028. Typically, multiple low stress overtravelstops can be associated with a MEMS device. For purposes of the hereinexposition, the first portion 102A and the second portion 1028 of thelow stress overtravel stop or low stress bump stop, on occasion cancollectively be referred to as overtravel stop 102 or bump stop 102.While overtravel stop 102 or bump stop 102 has been depicted ascomprising two portions (e.g., first portion 102A and second portion102B), overtravel stop 102 or bump stop 102 can comprise more than twoportions, and some embodiments can have multiple facets.

Also depicted in illustrative embodiment 100 is a proof mass (PM) 104that can be coupled to a first anchor point 108A and a second anchorpoint 1088. The proof mass 104 can be coupled to the first anchor point108A via a first elastic object that stores mechanical energy 106A, suchas a first spring. The proof mass 104 can also be coupled to the secondanchor point 108B via a second elastic object that stores mechanicalenergy 1068, such as a second spring.

Additionally, as illustrated in embodiment 100, the overtravel stop 102can be affixed to a third anchor point 108C. In regard to affixing theovertravel stop 102 to the third anchor point 108C various reactiveand/or nonreactive adhesives and/or attachment mechanisms can beutilized, such as various resins, mechanical fasteners, and the like.

In some embodiments, overtravel stop 102 can be affixed to the thirdanchor point 108C via the first portion 102A of the overtravel stop. Inother embodiments, overtravel stop 102 can be affixed to the thirdanchor point 108C via both the first portion 102A and the second portion102B of the overtravel stop. In yet further embodiments, overtravel stop102 can be affixed to the third anchor point 108C via the second portion1028 of the overtravel stop 102.

As noted earlier, overtravel stop 102 can comprise a first portion 102Aand a second portion 1028. In some embodiments, the first portion 102Aof the overtravel stop 102 can be substantially planar in a directionapproximately orthogonal to a motion of the proof mass 104 when theproof mass 104 is initially set in motion. For instance, where proofmass 104 is initially set in motion around a first axis (e.g., anx-axis) the substantially planar first portion 102 of the overtravelstop 102 can be aligned approximately parallel to an edge of the proofmass 104 as the proof mass 104 moves around the first axis.

It will be noted with regard to FIG. 1 that the proof mass 104 when atrest and/or when initially set in motion is not in contact with anyportion of the overtravel stop 102. In particular, proof mass 104 atrest and/or when initially set in motion is typically not in contactwith either the substantially planar first portion 102A of overtravelstop 102 or the second portion 1028 of overtravel stop 102.

In regard to the second portion 1028 of overtravel stop 102 it will beobserved that this portion of overtravel stop 102 can be formed orshaped to match to one or more polynomial function representing at leasta group of constants and at least a group of variables. Thus, the shapeof the overtravel stop 102 inclusive of the first portion 102A and thesecond portion 1028 can be an approximately planar first part (e.g.,first portion 102A) that seamlessly transitions into a shape thatcorresponds (e.g., is substantially consistent) with one or moregenerated polynomial function comprising one or more constant numericvalues and/or one or more variable numeric values. For reasons that willsubsequently become apparent, the polynomial function can be selectedfrom one or more groupings of polynomial functions that can ensure thatas proof mass 104 moves and gains in acceleration rotating about a firstaxis the proof mass 104, once it contacts the substantially planar faceof the first portion 102A, it will rapidly migrate, due to theincreasing acceleration of the proof mass 104 about its axis ofrotation, from the substantially planar surface of the first portion102A of the travel stop 102, traverse the more curvilinear surface ofthe second portion 102B of the overtravel stop 102, and ultimately freeitself from the surface (e.g., both surface of the first portion 102Aand the surface of the second portion 1028) of the overtravel stop.

In regard to the surface of the overtravel stop 102 (e.g., first portion102A and/or second portion 102B) can comprise any of silicon,poly-silicon, titanium, germanium, silicon oxide, silicon nitride,tungsten, and titanium oxide. Further in relation to the curvilinearsurface of the second portion 102B of the overtravel stop 102, thecurvilinear surface can have an aspect ratio that can be approximatelyequal to or greater than 1:5.

As will be observed by those of ordinary skill, as poof mass 104transitions from the substantially planar surface comprising the firstportion 102A to the more curvilinear surface comprising the secondportion 1028, the edge of the proof mass 104, when it comes into contactwith the curvilinear surface of the second portion 1028, can have apoint contact with the curvilinear surface of the second portion 1028.More particularly, when the edge of proof mass 104 is in contact withthe curvilinear surface of the second portion 1028 of the overtravelstop 102, the contact point can be a tangential point on the curvilinearsurface that can be determined as the result of differential of the oneor more polynomial function that can have been used to form thecurvilinear surface of the second portion 102B. In contrast, when theedge of proof mass 104 contacts the substantially planar first portion102A of the overtravel stop 102, the result of a differential of thesubstantially planar surface should tend to be approximately zero.

By using an overtravel stop comprising a first portion 102A that has asurface that can be relatively planar and a second portion 102B that canhave a curvilinear surface that conforms to one or more polynomialfunction stiction can be avoided, reduced, and/or mitigated. Stiction istypically an undesirable situation which can arise when surface adhesionforces are higher than the mechanical restoring force of a MEMSstructure or MEMS device. Stiction is recognized to often occur insituations where two surfaces with areas in close proximity come incontact. The greater the contact area at both macroscopic andmicroscopic roughness levels, the greater the risk of stiction. At amicroscopic level, soft materials can deform, effectively increasingcontact area. Surfaces can be unintentionally brought into contact byexternal environmental forces including vibration, shock and surfacetension forces that can be present, for example, during aqueoussacrificial release steps often used in micro-fabrication processes.Adherence of the two surfaces can occur causing the undesirablestiction.

In the embodiment depicted in FIG. 1 it should be noted the proof mass104 has not be set in motion through the imposition of an external load,and as such proof mass 104 is not in contact with the overtravel stop102. Further, it should also be noted that in many embodiments theovertravel stop 102 can be situated on one or more axes (e.g., x-axis,y-axis, z-axis). Also it should be observed, that, multiple sensingelements, or multiple sensing devices, can be situated proximately toproof mass 104 to measure the motion of proof mass in the one or moreaxes. For example, as depicted in FIG. 1 , a first sensing element orsensing device 112A can be located between proof mass 104 and an anchorpoint 108A, and a second sensing element or sensing device 112B can besituated between proof mass 104 anchor 108B. Additionally, it should benoted that proof mass 104 can be asymmetric in one or more direction.

FIG. 2 provides additional illustration of an illustrative embodiment200 of the low stress overtravel stop that can comprise a first portion102A and a second portion 1028 (now respectively labeled overtravel stop202 first portion 202A and second portion 202B). As noted above,multiple low stress overtravel stops, such as overtravel stop 202, canbe associated with a MEMS device. In this depiction it will be observedthat an edge of the proofmass 204 has contacted overtravel stop 202 onthe approximately planar surface of the first portion 202A. The edgecomprising the overtravel stop 202 can have come in contact with theapproximately planar surface of the first portion 202A of the overtravelstop 202 due to an external force or external load having earlier beenimposed on proof mass 104 (now 204). The external force or external loadexerted on proof mass 104 can have caused proof mass 204 to be set inmotion around one or more axes (e.g., x-axis, y-axis, and/or z-axis).

In the embodiment depicted in FIG. 2 , proof mass 204 can have been setin motion, by the external force or external load in the y-axis, suchthat proof mass 204 has accelerated to such an extent that it has comein contact with the overtravel stop 202 and more particularly with theapproximately planar surface of the first portion 202A of the overtravelstop 202. At this point in time the effects of stiction can come intoplay since the approximately planar surface of the first portion 202A ofthe overtravel stop 202 can provide sufficient surface for the motion ofproof mass 204 to adhere to the first portion 202A of the overtravelstop 202. Nevertheless and in accordance with the subject disclosure, asthe external force or external load about the one or more axes isincreased, the proof mass 204 can transition off the first portion 202Aon to the second portion 202B of the overtravel stop 202, therebyovercoming the effects of the stiction that can have caused proof mass204 to adhere to the overtravel stop 202, and eventually releasing(e.g., via an un-zippering/skittering effect) proof mass 204 from theovertravel stop 202.

In regard to FIG. 2 , the first elastic object that stores mechanicalenergy 106A and the second elastic object that stores mechanical energy1068 illustrated in FIG. 1 are now depicted as first elastic object thatstores mechanical energy 206A and second elastic object that storesmechanical energy 206B. Further, first anchor point 108A, second anchorpoint 1088, and third anchor point 108C are now represented as firstanchor point 208A, second anchor point 208B, and third anchor point208C. For example, as depicted in FIG. 2 , a first sensing element orsensing device 212A can be located between proof mass 204 and an anchorpoint 208A, and a second sensing element or sensing device 2128 can besituated between proof mass 204 anchor 208B

FIG. 3 provides further depiction of an illustrative embodiment 300 ofthe low stress overtravel stop 202 that can comprise a first portion202A and a second portion 202B (now respectively labeled overtravel stop302, first portion 302A and a second portion 302B). In this embodimentit will be observed that the proof mass 304 has shifted off thesubstantially planar surface of first portion 302A to the morecurvilinear surface of second portion 302B. The cause of the shift ofthe proof mass 304 from the substantially planar surface of firstportion 302A to the more curvilinear surface of second portion 302B canbe an increase in the external load imparted to proof mass 304 causingproof mass 304 to accelerate around its axes of rotation. Thus, as theacceleration of the proof mass 304 increase about its axes of rotation,proof mass 304 migrates across the curvilinear surface of the secondportion 302B, making point contact with the curvilinear surface as proofmass 304 traverses over the curvilinear face of the second portion 302Buntil proof mass 304 frees itself from the stiction forces that can havecause proof mass 304 to come in contact with the low stress overtravelstop 302.

In the context of FIG. 3 , the first elastic object that storesmechanical energy 206A and the second elastic object that storesmechanical energy 206B illustrated in FIG. 2 are now depicted as firstelastic object that stores mechanical energy 306A and second elasticobject that stores mechanical energy 306B. Further, first anchor point208A, second anchor point 208B, and third anchor point 208C are nowrespectively represented as first anchor point 308A, second anchor point308B, and third anchor point 308C. For example, as depicted in FIG. 3 ,a first sensing element or sensing device 312A can be located betweenproof mass 304 and an anchor point 308A, and a second sensing element orsensing device 3128 can be situated between proof mass 304 anchor 308B

FIG. 4 provides an additional example embodiment 400 of a low stressovertravel stop comprising a first portion 402A and a second portion402B. The first portion 402A and the second portion 402B, wherenecessary, can collectively be referred to as overtravel stop 402. Aswill be noted by those of ordinary skill, in various embodiments,multiple overtravel stops comprising first portion 402A and secondportion 402A can be associated with and/or incorporated within MEMSdevices. Further, in various embodiments, overtravel stop 402 can becoupled to an anchor point 410A via various reactive and/or nonreactiveadhesive and/or various attachment mechanisms.

As illustrated, overtravel stop 402, like overtravel stop 102 (andovertravel stop 202 and overtravel stop 302) described and depictedabove, can comprise a first portion 402A and a second portion 402B,wherein the first portion 402A can have a surface that has a profilethat is substantially planar, and wherein the second portion 402B canhave a shaped surface comprising a profile that is substantiallycurvilinear and that conforms to one or more polynomial functionrepresentative of first groups of constant numerical values and secondgroups of variable numerical values.

Also depicted in FIG. 4 is a proof mass 404 that can comprise a firstportion 404A and a second portion 404B. The first portion 404A andsecond portion 404B can be coupled to one another via a first elasticobject that stores mechanical energy, such as a first spring 406.Further, as illustrated, the second portion 404B of proof mass 404 canbe coupled to an anchor point 410B via a second elastic object thatstores mechanical energy, such as a second spring 408.

In regard to overtravel stop 402 comprising a first portion 402A andsecond portion 402B, in various embodiments the first portion 402A canhave a substantially planar (e.g., flat) surface profile in a directionthat is approximately orthogonal to a motion of the proof mass 404 whenproof mass 404 is set in motion. For instance, should proof mass 404 isset in motion around a first axis (e.g., x-axis, y-axis and/or z-axis)the substantially planar surface profile of the first portion 402A ofovertravel stop 402 can be aligned approximately parallel to the firstportion 404A of proof mass 404. For example, as depicted in FIG. 4 , afirst sensing element or sensing device 412A can be located between asecond portion 404B of proof mass 404 and an anchor point 410B, and asecond sensing element or sensing device 412B can be situated between afirst portion 404A of proof mass 404 and a second portion 404B of proofmass 404.

It will be noted and as depicted in FIG. 4 , proof mass 404 when at restand/or when initially set in motion does not contact with any portion ofovertravel stop 402.

FIG. 5 provides additional illustration of an example embodiment 500 ofa low stress overtravel stop 502 comprising a first portion 502A and asecond portion 502B. In this depiction the first portion 504A of proofmass 504 has contacted the first portion 502A of overtravel stop 502.The first portion 504A of proof mass 504 can have come in contact withthe substantially planar surface of the first portion 502A of overtravelstop 502 due to an external force or external load having been imposedon proof mass 504. The external force or external load exerted on proofmass 504 can have placed proof mass 504 in motion around one or moreaxes (e.g., x-axis, y-axis, and/or z-axis) and can have acceleratedproof mass 502 to such an extent that the first portion 504A of proofmass 504 contacts the substantially planar surface of first portion 502Aof the low stress overtravel stop 502.

When the first portion 504A of proof mass 504 contacts the substantiallyplanar surface of first portion 502A of the low stress overtravel stop502, the effects associated with stiction can come into play as thesubstantially planar surface of first portion 502A can providesufficient surface to the first portion 504A of proof mass 504 to causeproof mass 504 to adhere to the substantially planar surface of firstportion 502A. For example, as depicted in FIG. 5 , a first sensingelement or sensing device 512A can be located between a second portion504B of proof mass 504 and an anchor point 510B, and a second sensingelement or sensing device 5128 can be situated between a first portion504A of proof mass 504 and a second portion 504B of proof mass 504.

Nevertheless, as is illustrated in FIG. 6 , as the external force orexternal load about the one or more axes is increased, the first portion504A of proof mass 504 can gradually transition from the substantiallyplanar first portion 502A of the low stress overtravel stop 502 to morecurvilinear surface of the second portion 502B of the low stressovertravel stop 502, thereby overcoming and releasing proof mass 502from the stiction forces associated with the low stress overtravel stop502.

In the context of FIG. 5 in relation to FIG. 4 , it should be observedthat the first spring 406 and the second spring 408 have been relabeledas first spring 506 and the second spring 508. Similarly, anchor point410A and anchor point 4108 are relabeled as anchor point 510A and anchorpoint 5108.

FIG. 6 provides further illustration of an example embodiment 600 of alow stress overtravel stop 602 comprising a first portion 602A and asecond portion 602B. In this depiction the first portion 604A of proofmass 604, as a function of additional external forces or additionalexternal loads having been imposed on proof mass 604 around one or morerotational axes (e.g., x-axis, y-axis, and/or z-axis), has transitionedfrom the first portion 602A of overtravel stop 602 to the morecurvilinear second portion 602B of overtravel stop 602. First portion604A of proof mass 604 by transitioning to the more curvilinear secondportion 602B of overtravel stop 602 can now be in point contact withovertravel stop 602. Further, the first portion 604A of proof mass 604,by transitioning to the more curvilinear second portion 602B ofovertravel stop 602, can tilt toward the second portion 604B of proofmass 604. The point of contact by the first portion 604A with the morecurvilinear second portion 602B of overtravel stop 602 can be determinedby differentiating the one or more polynomial function that can havebeen employed in forming the surface of the curvilinear second portion602B of overtravel stop 602. Ultimately, when sufficient external forcesor additional external loads have been imposed on proof mass 604 aroundone or more rotational axes, the first portion 604A of proof mass 604can free itself off overtravel stop 602 entirely. For example, asdepicted in FIG. 6 , a first sensing element or sensing device 612A canbe located between a second portion 604B of proof mass 604 and an anchorpoint 610B, and a second sensing element or sensing device 612B can besituated between a first portion 604A of proof mass 604 and a secondportion 604B of proof mass 604.

In regard to FIG. 6 in relation to FIG. 5 , the first spring 506 and thesecond spring 508 are now represented as first spring 606 and the secondspring 608. Similarly, anchor point 510A and anchor point 5108 are nowdepicted as anchor point 610A and anchor point 6108.

As used in this application, the term “or” is intended to mean aninclusive “or” rather than an exclusive “or”. That is, unless specifiedotherwise, or clear from context, “X employs A or B” is intended to meanany of the natural inclusive permutations. That is, if X employs A; Xemploys B; or X employs both A and B, then “X employs A or B” issatisfied under any of the foregoing instances. In addition, thearticles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. In addition, the word “coupled” is used herein to mean direct orindirect electrical or mechanical coupling. In addition, the words“example” and/or “exemplary” are used herein to mean serving as anexample, instance, or illustration. Any aspect or design describedherein as “example” and/or “exemplary” is not necessarily to beconstrued as preferred or advantageous over other aspects or designs.Rather, use of the word exemplary is intended to present concepts in aconcrete fashion.

What has been described above includes examples of the subjectdisclosure. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe subject matter, but it is to be appreciated that many furthercombinations and permutations of the subject disclosure are possible.Accordingly, the claimed subject matter is intended to embrace all suchalterations, modifications, and variations that fall within the spiritand scope of the appended claims.

In particular and in regard to the various functions performed by theabove-described components, devices, systems and the like, the terms(including reference to a “means”) used to describe such components areintended to correspond, unless otherwise indicated, to any componentwhich performs the specified function of the described component (e.g.,a functional equivalent), even though not structurally equivalent to thedisclosed structure, which performs the function in the hereinillustrated exemplary aspects of the claimed subject matter.

The aforementioned systems have been described with respect tointeraction between several components. It can be appreciated that suchsystems and/or components can include those components or specifiedsubcomponents, some of the specified components or subcomponents, and/oradditional components, and according to various permutations andcombinations of the foregoing. Subcomponents can also be implemented ascomponents communicatively coupled to other components rather thanincluded within parent components (hierarchical). Additionally, itshould be noted that one or more components may be combined into asingle component providing aggregate functionality or divided intoseveral separate subcomponents, and any one or more middle layers, maybe provided to communicatively couple to such subcomponents in order toprovide integrated functionality. Any component described herein mayalso interact with one or more other components not specificallydescribed herein.

In addition, while a particular feature of the subject disclosure mayhave been disclosed with respect to only one of the severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and advantageousfor any given or particular application. Furthermore, to the extent thatthe terms “includes,” “including,” “has,” “contains,” or variantsthereof, and other similar words are used in either the detaileddescription or the claims, these terms are intended to be inclusive in amanner similar to the term “comprising” as an open transition wordwithout precluding any additional or other elements.

What is claimed is:
 1. A microelectromechanical system device,comprising: a proof mass coupled to an anchor via a spring, wherein theproof mass moves in response to an imposition of an external load to theproof mass; and an overtravel stop comprising a first portion and asecond portion, wherein the proof mass contacts the first portion of theovertravel stop and the proof mass becomes disengaged from the secondportion of the overtravel stop in response to the external load beingabove a first threshold value and below a second threshold value, andwherein the first portion of the overtravel stop is contiguous with andabuts the second portion of the overtravel stop.
 2. Themicroelectromechanical system device of claim 1, wherein the proof masscontacts the second portion of the overtravel stop and disengages fromthe first portion of the overtravel stop in response to the externalload exceeding the second threshold value.
 3. The microelectromechanicalsystem device of claim 1, wherein the proof mass moves in a firstdirection in response to the external load being less than a thresholdvalue, and wherein the proof mass moves in a second direction when theexternal load exceeds the threshold value.
 4. The microelectromechanicalsystem device of claim 3, wherein the first direction is a firsttranslation or first rotation, and wherein the second direction is asecond translation or a second rotation.
 5. The microelectromechanicalsystem device of claim 3, wherein the first direction is orthogonal tothe second direction.
 6. The microelectromechanical system device ofclaim 3, wherein the overtravel stop is located on an axis of the seconddirection.
 7. The microelectromechanical system device of claim 3,wherein the proof mass is asymmetric about an axis of the seconddirection.
 8. The microelectromechanical system device of claim 1,wherein the second portion of the overtravel stop is curved and has anaspect ratio greater than 1:5.
 9. The microelectromechanical systemdevice of claim 1, wherein a surface of the overtravel stop comprisesany of silicon, titanium, germanium, silicon oxide, silicon nitride,tungsten, or titanium nitride.
 10. The microelectromechanical systemdevice of claim 5, further comprising a first sensor and a secondsensor, wherein the first sensor measures a first motion of the proofmass in the first direction, and wherein the second sensor measures asecond motion of the proof mass in the second direction.
 11. Themicroelectromechanical system device of claim 1, wherein the anchor is afirst anchor, and wherein the overtravel stop is coupled to a secondanchor.